1. Field of the Invention
The present invention relates to an illumination apparatus for testing a photoelectric transducer device.
2. Description of the Prior Art
Recently, solid-state image sensor devices such as a CCD (charge-coupled device) have become highly developed. This has led to a demand for a high-performance illumination optical system for testing such devices. Such an illumination optical system must first provide uniform light illumination. Second, the illumination optical system must have a high-resolution imaging unit for highly precisely testing small pixels of a solid-state image sensor. Third, the illumination optical system must have a function to vary the intensity of light and a function to switch test patterns at high speed. Various conventional techniques have been proposed to achieve uniform light illumination by a method using a diffusing plate or an integrating sphere, a Kohler illumination method using a microscope or the like. However, it is difficult to obtain uniform illumination having an error within several percentages. In addition, uniformity of emission illuminance distribution is generally limited, so that the light rays used for uniform illumination must be constituted by a minimum range of light rays. However, since the effective numerical aperture NA of a projection optical system is decreased, sufficient resolution cannot generally be provided. Uniform illumination has a contradictory relationship with high resolution. It is difficult to satisfy both uniform illumination and high resolution. In general, high-speed operation must accompany a compact arrangement of various optical elements and the illumination optical system. In order to test various types of optical elements, high-luminance spot illumination as well as uniform illumination is required. Demand has arisen for an apparatus which may be easily switched between uniform illumination and high-luminance spot illumination at high speed. In order to incorporate an illumination apparatus of this type in a fabrication line of semiconductor elements such as solid-state image sensors, the illumination apparatus as a whole must be small in size.